At the end of this article there is a REALLY interesting take on who Cumberbatch's villian is. It includes some spoilers, so consider yourself warned!
It could be that Abrams planted the "April's Gun" on the set for misdirection, but everything else the writer sells is pretty solid. Could be that Weller plays an older April in a flashback scene, when we learn how he got himself young again. Maybe his wife dies and he blames Starfleet. Cumberbatch could be using "John Harrison" as an alias so no one recognizes him.
It's an interesting theory, especially for those who consider TAS "canon".